Process for the production and purification of sulphur dioxide



April 9, 1935. w 1555 1,996,764

PROCESS FOR THE PRODUCTION AND PURIFICATION OF SULPHUR DIOXIDE Filed April 4, 1953 flcz'd Preheafer Coke 50 10 the carbon lost in the reaction;

1 v Patented Apr. 9, 1935 r i I I PROCESS FOR THEAPRODUCTION NDPURJ- FICATION F SULPHURVDIIOXIVDEQ William Morris Hibbs, Wilmington; NJ}. 7

- "ApplicationAprilei, 1933, SerialvNo. 6 64,415 v H e TClaims'. 101. 23- 177); I p p The invention relates generailytcthejproduce p s Th sj e se -bed by. h r ac d,- tion; of;sulphur"dioxide which in tum maybe just asin' the usualcontact s'ulphuricacid plants. converted into sulphuric-acid, and more partic 'fil i e P h6 l p fl a ularly to the production of sulphur diOXidBQbY- en sdo 1 a b 1 9. 11 1 material '5 the treatment of weak or spent acids which have the dseaq d' v -t e dec m s i n Q -th a been separated tram-the original sludge; by heatd;' o provision whatever vin ing such weak acids with a quantity of "carbon; "been m d r I91 acids 9 in carbon 9 the supply 'ofwhich may-beareplenishedirom' su hde qmp it qn eac n V t V, b time to time as-requiredfor the replacement of xeme r p s d- "e hod only has tbeenip 'sible toycompletel'y decompose'all of any spent, 10 The process relates espeeiallyto theproduction s ud e qrwaste ecidixsulphuriw i anydeeree of a. sulphur dioxiderrom-wmeh;maybe ,pro! 'B- mgflf 1 continuous Q r Pm 'W ih-Q duced a water-white, commercially": pure ;sul- 91 3 391 i t a W PhW Q d I not phuric acid from sludge, spent or'waste sulphuras s hur {d oxi e e e i r t t e e 15 16 in acid which has been previously separatedifrom QmP n-*V i '1: i the original sludge and Vwhichz-has a concen 5 zmt e mq -dea s-P r -we tration of from 20.110 48 B., depending on the s s s q -wlbhuaqi wh beh Separated origin of the original sludge. andrnethod 'em- I r m P? 9 i19 B 8 which Dloycd in separation, r I c vam t rd i y r m 2 to B a 20 Heret-ofore ithasbeen concentrated either by pi' P e n a in? 1 h a m x m direct or indirectheatto a maximum coneentra- C t mi of 66 by a y KIIQWH 1 4 tion of 66? Be. I-Iigher concentration: by these :11 -Y i=1" i i methods was impossible due'to the decomposi-v Sp nt u g Q- 5 i 9 1 9 9 1* tion of the acid at hightemperaturei by th m; tent are un lm the explosives industry, nd

purities Present, chiefly carbonaceous material; l enfie e net/ i the ea 25v In viewxof the ever'increasing'demand for sul- V merit of 'tm ..1 e s o at ti h fi ifi is phuric acid of a strength above 66 B and of n d J flCl P acids heretoiore suflicient purityrto permit of its use the varion t a e mu of y either ous industries, huge sums of money have been director fi es atv spent for research in an endeavor to produce a (Due to the th-pfcentagof car'- T it cheaper and purer acid from" sludge; spent or 0 1 i r ouse p e i' e t Sludge t wastacii j Y i l V acidait has heretoforebeen impossibleto govern Methods have been-developed whereby the W w fi flf cfn f m such a e sludge'spent or waste acid has beendecomposed K: 1 1331193159130 the Varymg by heatwith 'theformation of sulphur-dioxide. @F e P Such -i it impos- This decomposition product was to be reoxidized Slble t a emr a mgne s 'd q p s e by suitable means to form sulphuricfacid. {By out d n l i l il let 'eu h i acldwhich no known previously developedmethod, however, P PPP e mm calfbon 6561115 f has a continuous operation been offered the m t t 3 e -t e rate of decomposition and '40 manufacturer or has any method thus far disthe t i n f l l h acid which was "105% -1 losed provided for a'complete decomposition of h purification mo c b witht e the acid in the event insufficient carbonaceous 7 5 1 .9 113 Qntinuous Operating cycle, has material was contained in the separated, Spent been overcome by the proposed'methodas herein sludge or waste-acid. a r described.-' r I For years it has been known that sludge or i. defi i i mr o e o d must 45 f spent sulphuric acids high in carbon couldbe be m intained at. all times if'c p bflp ecomposed by heat with'the liberation of su1-, sition o the sludge, spentfior'waste acidisto phur'dioxide (SOzLf-As early as the year- 1899 progress ylininterruptedrwithout 'di-stillation of Y processes were developed covering "the manufac-- ulphuric. acid.

I ture of sulphuric acid from oil refinery sludge. In maintain continuous Operation 7 The process then describedwas based on the with a definite minimum ratioof carbonto acid,, fact thatwhen heated, oilreiinery sluclge'decom- I haveperfecteid a method which, by; the aid of posed, liberatingwatenhnd sulphur dioxide;-v lhe' a decomposition chamber where'there is atall sulphur dioxide was passed over a catalyst where timesfan excess of carbon present, thus assures conversion into sulphur tri'oxide was accomcomplete decomposition of theseparated, spent,

sludge or waste acid without fear or distilling on any of the sulphuric acidwhich wouldj result in lower yields and increased operating costs.

cess carbon," the temperatures and the. proportions of the reacting materials being so regu lated that .a1l sulphuric.acid or .sulphuric..acid compounds containedinsuch acids will g'beilib'er- 'ated in the form ofsulphur dioxidelSOz) This fmethod'has been developed and perfected-with the idea of utilizingweak acids such as sludge or spent acids in the manufacture ofeither chamber j acid or contact sulphuric acid, The purity-from V ,concentrated ,acidfof a strength equal to 109% carbon contamination of such acidfas is produced by the present process depends "largely on the fact that preferably no agitation is-'employedfduring j. decomposition. Thus there'is avoided the ex- 'cessivevolumefof carbon dust consequent uponagitationi which in-other processes has tob'e either scrubbed from the gases; or; burned.---

The fact that previously separated -sludge or 1 spentacids'are us'e'di'n.th'ep'rocess is o'f 'vital- :im:

gsary'for-producing a commercial .acid pf high .puri-tyi The removal of volatile hydrocarbons,"

65. a "thoroughly saturatedwith 'acid;sufliciently con centrated to react with the carbon,'-th'us produc- 1 portan'ce when considering the purification necest'ars. and Y alcohols byprevious separation enables a the" production of an acid" offhigh purity at much lower cost'than chum otherwise be' obtaiiied with' -i foutthe necessity of elaborate purification equip; ment.'-I'r 1 view offthe class of acids' 'hereinf e-a ferred-to'being -tOQ low in carbon to decompose by heaflWithiiflt di's ti lling" Off most "of the avail able sulphuric' acidas acid ratherthan as' 'sul: I phur dioxide-, the importance of addingPthespent acids to a mixturesufliciently'high'irr carbon-to: V 7 promote rapid-decomposition I becomes 'apparen Periodicadditions of carbon to "the decomposing mixture are necessary for the replacement :of carbonrlost in the reaction;

Previous to'the development of jthepresent" process, all. separatedjsludge or spent" acids of I "pump; if fuel oil isnsed as'a medium of heat; and the 1 high power cost customarily encountered is low carboncontent'have-been concentrated-either carbon and' heat' as herein described: "Heretofore, so far 'as'Iam aware, no one has attempted to addweak separated'sulphuric acid to 'amixture of carbon and "acid; whichimixture is already in a state ofdecomposition: V p Continued experiments have demonstrated the fact that 'fwhen' sulphuri acid andca'rb on are heated tdtemperatures*between 235' and'2601 Cg, and preferably etween 250 and 260 1G,, decomposition ofi'the sulphuric' acid takes placewith the formation or sulphur dioxide and water: Inthe presentproc'ess advantage is takenof this're action by' adding separated sludge or spent sulphuricacid'to alarge excess of carbon which is already'heatedto the desiredj'tempe'raturej and. is

ing the desired decomposition-. "-fAddition oficarplus slight mechanical losses;

ban to the decomposing mixture. may be necessary-for replacement of carbon lost in the'reaction l My experiments have further 1 demonstrated the fact that the desired concentration necessary for'this reaction can be maintained-by accurate temperature control while the continuo'usiricom ing spentor sludge acid is constantly liberating its water and replacing the decomposing acid so that acontinuous operation is maintained.

.By controlling the temperature and volume of the-incoming acid, it has been demonstrated that it is possible to successfully recover all available "the costof storage tanks, labor, acid yields, etc. effected by the presentprocess', which eliminates the necessity for dealing with 66 B. acid when a H280 is desired, will be apparent. --a"1he'*gaseous products of decomposition pass ,OVerto'asorubbing and cooling system where water vapors fromrthe reaction are condensed. and

then reci'rculated over thescrubbing and cooling towers for the purpose of removing any particles ofcarbon carried over mecl' anically by the products ofjdecomposition. The heat of the incoming gas issufiicient to liberate the sulphur dioxide from the scrubbing water, thus permitting the excess water to'passto a drain free from acidor acidformingcompounds. The number of cooling and'scrubbing-towers used may be varied, depehdinglon conditions encountered.

A gdi'sti nct' advantagepifered by the preferred process. yvherein indirect heatis employed is the almostcomplete absenceof carbon dust as wellas other impurities encountered when unseparated sludge' or spent sulphuric acid is' decomposed by heat for the-purpose of producing concentrated sulphuric, acid, Additional advantages; offered a'rz-lbwrinitialcost of construction and subsequent operationg the total absence of mechanical agitation or other moving "equipment with the exception; ofasmall pump for the .purpo'seof circulating the condensed water for'purification purposes; and..poss'ibly a small oil-circulating f requires less complicated and elaborate purificae .tionztreatment, neverthelessdirect heat may be employed-if desired,i,without departing from the spirit-of the invention in its broadest aspects. Thus'for. direct heating, hot air either direct from the combustion of 'oil or gas, or air previously preheated but free from other products of com bustion, .may; beemployed to supply the necessary heat'for thereaction. The direct heating process is somewhat'more economical from the standpoint of fuel consumption, but. on account-of the agitation involved the gas ma under; certain conditions carry over with it some finely divided carbon which can be removed only with some difficulty, Direct heating by hot air or' waste gases also reduces the concentration of the gas.

Afterthe decomposition of the weak acids into sulphur dioxide, the gas may be purified and then reoxidized by a .catalystiinto sulphur trioxide. The trioxidemay then be absorbed inthe same manner customarily employedin contact plants for conversion into, sulphuric acid... In case the chamber method is employed; the dioxide would preferably be oxidized by'the'oxides of nitrogen derived. either from the potting of sodium nitrate or from an ammonia oxidation process. r

Referringtolthe'drawing, the numeral'l denotes. -a gas ,or 'oil burning. furnace, composed pipe and into thecon densate tank is by gravity,

v. thelevel ofethe tank 24 being .sufficiently low for 1 The sulphur this purpose? sired; ext'entwith air; passfrorngthe upper end. of

with a contact or chamber. 'plant, no separate means forexhaustingthe fumesis herein shown, I

it being intended that the equipment customarily employed'in the contact orchamber plant; shall be utilized.-

i' L 2 a. It .will'also be'understood that the operationiof; the present apparatus is not limited tothe use of- V one stillor decomposition chamber. One, two or asmany as requiredgmay be employed. Where ingtothescrubbingtower .l8.' V A in molecular ratio. .Expr,essed in-termsof percenmore' .than oneQstill is used; twoor morezsuch stillsmay discharge into; a commonheadergleade peratureofthe'furnacer=- My. experiments have shown thatcomplete de-' composition of the sulphuricacid to sulphur, di-' oxide does'not occur if the ratio of, carbon tozacid is less than-onepartcarbonto two parts-mee V ta'ge, the ratio oicarbon to acid,isi5=7692%-care bon" to 94.2308%'-.H2S.O4,.or. a molecular'ratio of."

Consequently in operatingmy,processthe'still 2 contains a .mixture'of carbon andconcentrated sulphuric, acid, jthere being-maintained :at-- all times an excess] oflxpart 1( molecular) carbon to two; parts-(molecular) H2504. :{The mixture is continuously maintained atzabout the level 2. by'

the additionoi acid through the pipe 10 from the,

acid preheaters: to compensate ,for theigasespass= ing oiT through pipeli, thecarbon supply' being, replenished from time to-timethrough the:open

ing Has requi cess. I Theacid ed by the hot. jumes rfrom thefurnace lion their way tor-the stack; the =portionwhich enters the separatedaacidused. V I -.The concentration of t e weak'acid asaddedto the: still is considerablyqbelowith'e point'where it will react at once, with the carbon ;pres'ent;'and consequentlythe quantity of weak acid added must 'be;accurately controlled so that -just;suffi.-. cient acid isadcled to 'replacethe acid reducedrby. j thecarboni- Theiweak acid, incoming in contact with the large volume of concentrated acid in the' still,l is quickly mixed and-the water content 4 thereof vaporizedndistilling off alongwithth'e' sui-e phur dioxide gas produced by the reaction of the concentrated acid: and carbongin'. the still under the proper temperature; conditions Theresulting products of decompositionypassi'oif' inyapor and gaseous-statetotheipurification system.- A f continuous and uniformioperation of the process I r a is therefore dependent on the rate at iwhichweak acid added to thestill, the temperature main? dioxide ass. fdiifitdtb his des-.5

Itwill be understood. that ;t he. plant as herein. 7 described operates under. asuitabledegree of vac uum; but, as itis intended for -usein con-junction.

red: toqmaintainjthe necessary'E-ex supplied, to; the; preheating pans 1, -8 and 9 isaweak acidwhichhas-been separated from the original sludge and has :a; concentration of from 20 .to 48.B.,;depending on-the origin of s the original sludge and the :method employed in separation. This weak acidis progressivelyheatscrubbing and cooling towers.

by the temperature of the mixture as indicated by the pyrometer l3,,unlessthe pyrometer M in.- dicates a change in the strength of the acid added.

Thus it willbe observed that accurate control and uniformity of temperature are absolutely necessary for successfulacontinuous operation.

Anywide variationin temperature affects directlythe rate .ofjdecomposition. of the acid. Ex-

' perience has shown that at 25Q-260 C. decomposition progresses at a uniform rate, although some variation fr om these limits is permissible without departing fromtheinyentionq. By means of ,thetwo pyrometers I3 and 14 it is possible to maintain accurate temperature control ofthe contents of'the still 2. Pyrometer, vIii, located nearthe bottom of the still, indicates any change in quantity of -.acid added after the burner (either gas or oil), which heats the furnace has been adjusted totheoperating conditions. Any change in temperature recorded, by this pyrometerindicatesa variation inquantity of acid addedor'amount of fuel consumed. Another pyrom eter (not-shown)- serves as a control for the tem- Pyrometerid is locatedabove the'mixture acid and carbon-and is-afifected only by the tem perature of the products of decomposition. Any changeinstren'gth or acid added or any distillationof acid due ,to insufiicientcarbon willbe in-,

stantly indicated by. this pyrometer.

shown) is preferably attached to inlet line H a 'behind the valve, By means of such a gauge a close'controloi airentering at this point may be maintained; The remaining a quantity of, air re- .quired to reduce the concentration of the S02 gas to the desired'percenta'ge is'introduced into thesystem in the mixingtowerifl .through the value'controlled pipej l. f I V The.pyrometer l9 indicates-the temperature of the gaseous mixture entering the scrubbing'tower. Best .resultsfare obtained when gases enterthis point.;atapproximately'95f to 98 C. i In summer it may,.be-necessary.to spray water-on the lead line l5' from the still 2 to the scrubber l8, while inwinter this line may need insulation in order to maintain approximately these temperatures,

. Ihe 'temperatures of the 'gas leaving the r scrubber will be approximately to 0., While at the exit o fthejcooling tower they should be roximate The coke box or spray catcher may if necessary contain lead coolin'gc'oils if additional cooling is found necessary in order to secure a gas of not in excess of 20 C. for the entrance to the mixing toweni- Purification of thefisulphur dioxide gas is accomplished by passing the gas counter-current to the spray ofthecondensate entering the towers i3 and. 23 throughthevalves 29 and 3! The condensate-from the cooling tower and spray catchenmay in warm weather be cooled by any appropriatemeans before'recirculation overthe That portion of the condensate delivered to .the scrubbing tower cools andscrubs the incoming gas, then passes directly to the drain as all sulphur dioxide gas has been removedby' heat in the. lower zone, of the scrubber; Water will not absorb or retain sulphur dioxide in solution at the temperature of the because of the smaller volume ofgas handled I through scrubber and cooler, but also to lower the incoming gases. The bottom portion of the, scrubber i8 is a hot zone where the heat from the incoming gas releases from the condensate all' sulphur dioxide which may have been .previously absorbed in the upper orcooler zone, or

' any which the condensate carried over from the cooling tower.

The chief function of the cooling tower is the removal of as much moisturelas possible without added cost of operating. Cooling is accomplished by both'direct and surface cooling, and the major *portion of the spray carried along by the gas is V removedby the bubbles atlthe top of the tower.

The balance of the spray which'has been carried along with the gas is removed by the coke'box or spray catcher.

By thus removing all moisture carried over by mechanical means, the gas entering the mixing tower will contain only such' moisture as the temperature of the gas will permit facture of sulphuric acid from spent, waste or sludge acid where it hasv been possible. to secure a concentration of sulphur dioxide above 50%.

The value of this is at once apparent. Not only;

is it possible to reduce initial constructioncost cost of scrubbing and cooling the gas.v Cooling costs are items of considerable importance when large volumes of gas are cooled, hence the advantage of producing a concentratedgaswhich can be reduced to the desired concentration of 7 to 8% after cooling and removing the major portion of thewater. 1

What I claim is:

1. A continuous process for producing sulphur dioxide whichcomprises decomposing strong sulphuric acid in the presence of an excess-of carbon by means of heat, withdrawing the liberated sul-' phur dioxide gas, continuously adding weak spentv sulphuric acid of low carbon content derived from sludge and which has been, separated from the original sludge, in a quantity 'just sufiicientto compensate for the acid decomposed in the form of sulphur dioxide, and supplying additional carbon separate from theadded acid in order to' maintain the carbon excess at all times. 4

2. A continuous process for producing sulphur dioxide which'comprises decomposing strong sulphuric acid in the presence of an excess of carbonby means of heat, Withdrawing the liberated'suh phur dioxide gas, continuously adding weak spent sulphuric acid of low carbon content derived from sludge and which has been separated from the original sludge, in a quantity just suificient to compensate for the, acid decomposed in the form of sulphur dioxide, supplying additional carbon separate from the added acid in order'to maine tain the carbon excess'at all times, and maln- V 1 taining a temperature-of from 235 to 260" .C. I

during the reaction.

e 3. A continuous process for producing sulphur. dioxide with. comprises decomposing strong sulphuric acid'in the presence of an. excess of'carbon V by means ofheat, withdrawing the liberated sul- I phurdioxide gas, continuously adding weak spent f sulphuric acid 'of low carbon content derived from sludge and which has been separated from the; original sludge, in a quantity 'J'ustsuflicient to? compensate for the acid decomposed in the form.

of sulphur dioxide,- supplying additional carbon separate from the added acid in order tocmain tain the carbon excess at all times, andpreheating the spent acids prior to the decomposition reaction. I

4. A continuous, process for producing sulphur dioxide which comprises, decomposing strong sulphuric acid in the presence of an excess of carbon by means of hea.t; withdrawing the 'liber ated sulphur dioxide gas, continuouslyadding weak spent sulphuric acid of low carbon content derived from sludge and which has been separated from the original sludge, in a. quantity ju'st sufficient to compensatefor the acid decomposed. in thejform of sulphur dioxide, and supplying a additionalcarbon separate irom the added acidln order to maintain the carbon excess at all times,

the molecular ratio of carbon; to acid being main-" tained at not less than1to2;

5. A process of'decomposing separated sludge acid'which comprises treating weak acidseparated from-the original sludge, by {continuously adding said weak separated acid to a mixtureof hot concentrated acid and carbon, and decom-j" posing by means of heat in the presence of excess carbon, supplying additional carbonin orderto maintain said excess at all times, the tempera-f 'tures and the proportions of the reacting.ma-fterials being such that-all .thesulphuric acid or;

sulphonic acid compounds contained in such acids.

will be liberated in the form of sulphur dioxide.

6. A continuous process'whichcomprises heating strongsulphuric acid in ,the presence of a.

continuously maintained excessof carbon at a oxide, withdrawingthe sulphur dioxide and coni tinuously adding weak spent sulphuric acid of low carbon content in a quantity. just suflicient to compensate for the acid decomposed inthe form of sulphur dioxide 1 7. A process of decomposing spent sludge acid;

which comprises continuously adding weak'acid separated from theoriginal sludge to a' mixture of hot concentrated acid and carbon, heating the mixture inthe presence of excess carbon, main taining the temperatures and proportions of the, -60

reacting materials such that all sulphuric acid or compounds thereof ,will be decomposed to liberate temperature sufiicient to. give oif sulphur di 1 sulphur dioxide, and withdrawing and purifying;

the sulphur dioxide. r I WILLIAM jMORRIS'HIBBS; 

